In 1941, he took a job at MIT's Servomechanism Laboratory, where he worked on gun control systems until the end of World War II.
His work at M. W. Kellogg focused on rocket engine development, missile controls, and analog air defense systems.
In 1956, Marcy became Assistant Manager of Product Development at IBM's Corporate Headquarters in New York City.
Marcy left IBM in 1972 to do work as a consultant in the areas of engineering management, technology, and program review.
In 1974, President of the United States Richard Nixon nominated Marcy as Assistant Secretary of the Navy (Research and Development) and he subsequently held this office from October 15, 1974, until April 4, 1977.